Application of liquid chromatography–mass spectrometry in the determination of oxazaphosphorines and their metabolites

Rapid quantitation of cyclophosphamide metabolites in plasma by liquid chromatography–mass spectrometry

A method is described for the quantification of two metabolites of cyclophosphamide, specifically 4-hydroxycyclophosphamide (HCy), and carboxyethylphosphoramide mustard (CEPM). Plasma HCy is derivatized to the phenylhydrazone which is quantitated by LC-MS monitoring the chloride adduct of the derivative. The LLOQ based on material applied to the system is approximately 20 fmol. Plasma CEPM concentration is determined using LC-MS with a deuterated internal standard. Both assays have 50-fold dynamic range and require less than 4h to complete. The development of this rapid analytical method makes it feasible to adjust the dose of cyclophosphamide based on the pharmacokinetic disposition of HCy and CEPM in hopes of decreasing nonrelapse mortality in cancer patients.

Application of liquid chromatography-mass spectrometry to monitoring plasma cyclophosphamide levels in phase I trial cancer patients

A specific and efficient liquid chromatography-mass spectrometry (LC-MS) method was established for monitoring patient plasma cyclophosphamide levels in a phase I trial of an oral cyclophosphamide-based combination chemotherapy regimen. An Agilent 1100 Series LC-MSD system (Agilent Technologies, Avondale, PA, USA), with a single quadrupole mass detector using a positive atmospheric pressure chemical ionization (APCI) interface and single ion monitoring at m/z 261, was used. Chromatography was performed using a LUNA C8 5 microm 30 x 4.6 mm stainless steel column (Phenomenex, Torrance, CA, USA) and a mobile phase of aqueous acetonitrile pumped at a flow rate of 0.7 mL/min. High-throughput solid-phase sample extraction was performed using a Gilson ASPEC XL4 system (Gilson Medical, Middleton, WI, USA) controlled by prestored programs. The standard curve for cyclophosphamide was linear over the concentration range 0.026-1.08 microg/mL (r(2) > 0.994). Intra- and interassay accuracy and precision were 97-107 and 3-10%, respectively. The limit of detection was determined to be 0.01 microg/mL. Single ion monitoring at m/z 261 provided a high degree of specificity without interference from the matrix or other chemotherapy drugs. Automated sample processing allowed the analysis of a large number of plasma samples from a clinical trial of repeated daily oral dosing of cyclophosphamide. One hour after dosing, cyclophosphamide was detected in 98 of 106 plasma specimens at concentrations ranging between 0.03 and 4.88 microg/mL. Twenty-four hours after dosing, cyclophosphamide was detected in 72 of 77 plasma specimens at concentrations ranging between 0.06 and 3.13 microg/mL. There were no time-dependent changes in cyclophosphamide concentration during the 43 day period of repeated daily oral dosing. There was no correlation between cyclophosphamide dose and plasma concentration, despite the wide range of doses given in the clinical trial (50-125 mg/m(2)). We conclude that a solid-phase extraction LC-MS technique was validated for determining cyclophosphamide in human plasma. Interoccasion variability in the rate of oral absorption and in the clearance of systemically available drug may have contributed to the wide range of cyclophosphamide concentrations found at 1 and 24 h after tablet ingestion.